Electroforming as a self-organizing process of a nanometer gap in a carbonaceous medium

Analysis of the existing experimental data and proposed mechanisms and models for processes occurring in the electroforming of metal-insulator-metal (MIM) structures leads to the conclusion that the electroforming process includes the following two stages: the formation of a carbonaceous conducting medium of organic molecules as a result of the passage of current in the insulating gap, and the self-organization of the a nanometer gap in the conducting carbonaceous medium through bifurcation when the temperature of this medium locally exceeds a certain critical value on account of self-heating. It can be asserted that the nanogap is a dissipative structure which arises by virtue of the thermal instability of the carbonaceous medium when a stream of electrons is passed through it and the presence of a high electric field and which is stable on account the substantial nonlinearity of processes occuring in it which are involved in the feedback mechanism. It is shown that the initial conductivity of the structure which is necessary for carrying out electroforming can arise on account of the nanometer width of the insulating gap, and this is demonstrated experimentally on a so-called “open sandwich” MIM structure. Zh. Tekh. Fiz. 67, 39–44 (November 1997)     

Conductivity of nano-MIM diodes with a carbonaceous active medium in a model including percolation effects

A model proposed previously for processes in nano-MIM (metal-insulator-metal) diodes with a carbonaceous active medium is developed and refined. The inclusion of percolation effects in the insulating gap yields qualitatively new results and provides better agreement between the calculations and experimental data for physically reasonable values of all the parameters. An analysis of the model has made it possible to distinguish two different elements in the mechanism upon which it is based, which are important for understanding the essence of the processes that take place in electroformed nano-MIM diodes with a carbonaceous active medium: an internal negative feedback in the structure and modulation of the parameters of the cathode potential barrier. These elements show up in different ways in the observed characteristics of MIM structures. Zh. Tekh. Fiz. 69, 66–73 (November 1999)     

Conditions for the production of a single conducting nanostructure by electroforming

The process of electroforming (the production of a carboniferous conducting medium when the current flows through an organic material under a high electric field) in open sandwichlike structures with an insulating gap several tens of nanometers in width is considered. It is shown experimentally that there are factors that both favor (external ballast resistor) and prevent (local spreading resistance and the presence of the initial conductivity in the insulating gap) the production of a single conducting element between the electrodes. A simple model of the process in terms of the equivalent electric circuit is proposed. The model helps to find the trade-off between these factors and to construct an I-V diagram, which exhibits a region within which a single conducting nanostructure can be electroformed. An expression that relates the minimum permissible resistance of the nanostructure to its geometric parameters is derived.     

Electrical properties of the metal-insulator nanoparticles-metal structure

The electrical properties of the metal-insulator-metal (MIM) structure with a monolayer of Al₂O₃ or ZrO₂ spherical nanoparticles as an insulator have been investigated. It has been experimentally found that the MIM structure can be in a weakly conducting or highly conducting state, depending on the applied voltage. A phenomenon has been revealed that the differential resistance of the MIM structure is negative and approaches zero (reversibly) with an increase in the electric current. After treatment of the MIM structure in the medium of atomic oxygen or atomic hydrogen, the electrical conductivity of the structure increases and depends on the polarity of the applied voltage. It has been established that the differential resistance of the structure in the form of a monolayer of nickel and copper spherical nanoparticles located between the planar metal electrodes is positive and decreases with an increase in the applied voltage.     

Dynamics of magnetic insulation failure and self-organization of an electron flow in a magnetron diode

The dynamics of back cathode bombardment (BCB) instability in a magnetron diode (a coaxial diode in a magnetic field, B ≡ B _0z ≡ B ₀) is numerically simulated. The quasi-stationary regime of electron leakage across the high magnetic field (B ₀/B _cr > 1.1, where B _cr is the insulation critical field) is realized. An electron beam in the electrode gap is split into a series of bunches in the azimuthal direction and generates the electric field component E _θ(r, θ, t), which accelerates some of the electrons. Having gained an extra energy, these electrons bombard the cathode, causing secondary electron emission. The rest of the electrons lose kinetic energy and move toward the anode. Instability is sustained if the primary emission from the cathode is low and the secondary emission coefficient k _se=I _se/I _{e, BCB} is greater than unity. The results of numerical simulation are shown to agree well with experimental data. A physical model of back-bombardment instability is suggested. Collective oscillations of charged flows take place in the gap with crossed electric and magnetic fields (E × B field) when the electrons and E × B field exchange momentum and energy. The self-generation and self-organization of flows are due to secondary electron emission from the cathode.     

Temperature dependence of the current-voltage characteristic in a model of the conductivity of a metal-insulator-metal structure with a carbonaceous active medium

A new mechanism is proposed for the processes taking place in metal-insulator-metal structures with a nanometer-sized insulating gap. The dependence of the theoretical current-voltage characteristic on the substrate temperature is analyzed and compared with experimental results. Zh. Tekh. Fiz. 68, 139–141 (September 1998)     

Resonant tunneling of illuminated multi-insulator diodes

The current–voltage (I–V) characteristics of two different Metal–Insulator–Metal (MIM) diodes with three insulator layers were calculated and compared. The effect of illumination, or the photon-assisted tunneling was considered with the Tien–Gordon model. Our calculations indicate that, by carefully designing the insulating layers of the MIM diodes, the resonant tunneling phenomena can be tuned effectively in the diodes with quantum well structures. The results also show that the minimum shift of the illuminated current depends not only on the intensity of the photons incident but also on the diode structures, or the parameters of the insulators and so on.     

Heteroepitaxial growth of complex-oxide films from a self-organized system formed in a gas-discharge plasma

New experimental data on the characteristic features of the synthesis and crystallization of films of solid solutions of lead zirconate-titanate, deposited by means of rf diode sputtering of ceramic targets, are presented. Such a deposition system possesses threshold states, transition through which leads to a qualitative change in the processes occurring in the system and to the appearance of self-organization effects. The basic feature of this change is determined by the appearance of a new structured system, consisting of the sputtered particles and particles formed in the plasma, in the plasma of an rf discharge. Zh. Tekh. Fiz. 69, 87–91 (December 1999)     

Calculation of the critical conditions of instability in an electric field of a hemispherical droplet on a hard substrate

The critical conditions of instability of a hemispherical drop of a conducting liquid lying on a hard, electrically conducting substrate in an electric field parallel to the symmetry axis of the drop are found. These critical instability conditions are found to be higher than those of an insulating drop of the same size. Zh. Tekh. Fiz. 68, 9–12 (September 1998)     

Polaron defects in a charge density wave: a model for lightly doped BaBiO3

A model for BaBiO₃ was introduced by Rice and Sneddon, which treats this material as a simple three-dimensional version of a Peierls insulator, where the insulating gap is a consequence of the ordered distortion of the oxygen atoms. Charge accumulates on half the atoms and depletes from the other half. Experimentally, when holes are added to BaBiO₃ by doping, it remains insulating until a very large hole concentration is reached, at which point it becomes superconducting. In the Rice-Sneddon model, at large enough electron-phonon coupling, a mechanism for insulating behavior of doped samples is formation of small polarons or bipolarons which trap carriers in bound states in the Peierls gap. A variational calculation of the polaron binding in this model is given, and compared with “exact” numerical results on large clusters with periodic boundary conditions.     

Current in a high-current planar diode with a discrete emitting surface

The dependence of the current on emitter size is obtained for a high-current planar diode with a discrete emitting surface. It is shown that if the distance between the emitters appreciably exceeds their size, the dependence of the current on the ratio of the emitter size to the diode gap is a power dependence with an exponent of 3/2. The voltage dependence of the current obeys the “three-halves” law up to higher voltages than that for a planar diode with a homogeneous emitting surface. Zh. Tekh. Fiz. 69, 97–101 (June 1999)     

Electromagnetic excitation of infrasound in a conducting medium

A comparative analysis is made of the mechanisms of interaction between the electromagnetic fields of a global resonator and hydrodynamic and acoustic disturbances in a conducting medium. A universal boundary condition at the interface between air and the conducting medium, which takes into account the motion of the electrolyte, is obtained in an explicit analytical form to calculate the long-wavelength electromagnetic fields. The intensity of the electromagnetic field excited by a vertical hydroacoustic wave is estimated together with the efficiency of excitation of infrasonic oscillations of a conducting medium in the field of a global resonator. Zh. Tekh. Fiz. 68, 80–83 (January 1998)     

Anisotropy of the energy gap in the insulating phase of the U-t-t' Hubbard model

We apply a diagrammatic expansion method around the atomic limit () for the U-t-t ' Hubbard model at half filling and finite temperature by means of a continued fraction representation of the one-particle Green's function. From the analysis of the spectral function we find an energy dispersion relation with a modulation of the energy gap in the insulating phase. This anisotropy is compared with experimental ARPES results on insulating cuprates. Received 18 May 2000 and Received in final form 9 August 2000     

Insulating behavior of a trapped ideal Fermi gas

We investigate theoretically and experimentally the center-of-mass motion of an ideal Fermi gas in a combined periodic and harmonic potential. We find a crossover from a conducting to an insulating regime as the Fermi energy moves from the first Bloch band into the band gap of the lattice. The conducting regime is characterized by an oscillation of the cloud about the potential minimum, while in the insulating case the center of mass remains on one side of the potential.     

Enlargement of the band gap in the metal-insulator-metal heterowaveguide

We present a new metal-insulator-metal (MIM) heterowaveguide to enlarge the band gap, which is formed by alternately stacking two kinds of metals, modulating the MIM waveguide slit, and inserting different dielectric materials with the effective refractive index periodically modulated. Based on this structure, we adopt two different methods to enlarge the band gap: changing the thickness of the unit layer and combining two MIM structures. Both of them widen the band gap when surface plasmon polaritons propagate through the structure. This metal heterostructure is expected to have applications in surface plasmon polaritons (SPPs) based optical devices, such as filters, waveguides, especially for broad band gap elements.     

Stability of a charged drop of a viscous electrically conducting liquid in a viscous electrically conducting medium

A dispersion relation is derived for capillary oscillations of a charged electrically conducting viscous drop in an electrically conducting viscous medium. It is shown that aperiodic instability of the charged interface between the two media can arise in this system, with a growth rate that depends qualitatively differently on the ratio of their conductivities in different ranges of values of this ratio. In a certain range of conductivity ratios the drop undergoes oscillatory instability. Zh. Tekh. Fiz. 69, 34–42 (October 1999)     

Performance of W-InSb Metal-Semiconductor Point-Contact Diodes as Detectors and Mixers in the Near Infrared

Metal-Insulator-Metal (MIM) and Schottky-barrier diodes have been used extensively in the past years as harmonic generators and mixers for frequency measurements in the spectral range from the far-infrared to the visible. MIM diodes present a very low fabrication cost and are easy to handle, while Schottky diodes are mechanically more stable and long-lived. In the present work we discuss the performance of a metal-semiconductor point-contact diode for the radiation around 1 m. This device, which may be viewed as a hybrid between a MIM and a Schottky diode, combines the simplicity and easiness of fabrication of the MIM diode with the stability and the long contact life typical of the Schottky diode. It proved to be very efficient even for visible light.     

Study of the Insulating Magnetic Field in an Accelerating Ion Diode

The results of examination of the insulating magnetic field in an accelerating ion diode are presented. This field is produced in order to suppress the electron current and thus enhance the neutron yield of the D(d, n)³He nuclear reaction. The following two designs are discussed: a gas-filled diode with inertial electrostatic confinement of ions and a vacuum diode with a laser-plasma ion source and pulsed magnetic insulation. Although the insulating field of permanent magnets is highly nonuniform, it made it possible to extend the range of accelerating voltages to U = 200 kV and raise the neutron yield to Q = 10⁷ in the first design. The nonuniform field structure is less prominent in the device with pulsed magnetic insulation, which demonstrated efficient deuteron acceleration with currents up to 1 kA at U = 400 kV. The predicted neutron yield is as high as 109 neutrons/pulse.     

Model of current oscillations in a metal-thin insulator-semiconductor structure

A model is proposed for current oscillations in a metal-thin insulator-p-type semiconductor structure which are caused by the self-organization of carrier transport processes via insulator states. Zh. Tekh. Fiz. 68, 93–94 (December 1998)     

Adhesion of metals and semiconductors analyzed by a dielectric formalism

This paper discusses a model of the adhesive interaction of metals and semiconductors, based on a dielectric formalism and using the concepts of collective excitations — plasmons of the electron-ion system. Expressions are obtained in terms of the jellium model in the longwavelength approximation for the adhesion energy and the adhesive interaction force and are determined via the dispersion dependences of the energies of surface plasma oscillations for various materials whose surfaces are separated by a gap of arbitrary magnitude. The adhesion energies and the adhesive interaction forces are calculated for a number of simple and transition metals and semiconductors, and the adhesion characteristics are also obtained for the contact of the given materials with an insulating medium. Fiz. Tverd. Tela (St. Petersburg) 39, 964–967 (June 1997)